Surgical clips are medical instruments or implants which are temporarily used for pinching off or closing tissue perforations or are employed as vessel clamps for a medical long-term care for e.g. aneurysms. A multitude of different clips is known, for instance in the form of jaw-like clips in which the clamp or clip branches are formed to be curved in longitudinal direction similar to the upper and lower jaw and are coupled to each other at their two ends via a hinge.
Another example is represented by slim, elongated clips similar to conventional pliers, comprising two opposite clamping arms (branches) which are provided with teeth or a fluting and have their ends coupled to each other in the manner of a hinge.
The clips according to the prior art usually have two jaw parts coupled to each other in hinge-like fashion, said jaw parts each forming a clamping portion (in the following also referred to as a clamping arm or branch) and an operating portion. Further, the clips basically comprise a spring assembly which serves for preloading the clip into its closed position and brings about a clamping force which is exerted by the clip branches or clamping arms. There are clips in which the spring assembly is a separate component cooperating with the jaw parts of the clip, as well as clips in which the spring assembly is an integral component of the clip or of the jaw parts.
Aneurysm clips are known in which the branches or clamping arms are preloaded against each other by means of a U-shaped leg spring. The legs of such a leg spring either engage the clamping arms directly from outside or laterally and compress them, or they engage operating portions each prolonging the clamping arms in the longitudinal direction of the clip and compress them or pull them apart, depending on whether the jaw parts intersect or are parallel in the hinge area.
However, the use of a leg spring results in some disadvantages. Leg springs, in particular those comprising an energy storage means which is wound in spiral shape, usually require a comparably expensive and complex manufacture. In particular during the winding process, it has to be ensured that there is no cracking in the spring material. An excessive level of winding the leg spring is to be avoided, too, as otherwise the pressing force between the clamping arms may be reduced. All in all, the manufacture of leg springs requires a high level of precision in order to manufacture instruments whose attributes such as pressing force, durability, operational safety etc. are within a narrow range of tolerance.
A further problem in using leg springs is the provision of a reproducible pretensioning force. The leg spring has to be designed and dimensioned such that a predetermined pretensioning force is acted upon the clamping portions. This is decisive for the achievable maximum closing force. With predefined dimensions of the clip, it may be problematic to achieve the desired closing force which can be obtained at least a lot of times only with high efforts. It may also happen that there is a plastic deformation of the spring area, in particular in the case of a low number of windings or with a pure U-shape of the leg spring, with the number of windings ranging between 0.5 and 2 depending on the available installation space.
As a leg spring is usually arranged so as to be asymmetric relative to the branches of the clip or to its clamping arms, it may disadvantageously happen that frictional forces occur between the branches or clamping arms and the legs of the spring which cooperate with them. This results in a reduction of the maximum achievable closing force. In addition, the asymmetric arrangement may have the effect that the clamping arms of the clip do not open and close in parallel fashion. A further disadvantage is that there usually is only a linear contact between the legs of the spring and the branches.
From DE 10 2011 055 094 A1 an aneurysm clip is known which comprises a first jaw part including a clamping arm, a fork portion being formed on one proximal end region of said clamping arm. The clip further comprises a second jaw part comprising a clamping arm on whose proximal end a spiral spring is formed. The latter is inserted in the fork portion of the first jaw part and guided therein in such a manner that it is coupled to the fork portion in a torque-proof manner. This usage of a spiral spring avoids some of the afore-mentioned disadvantages of leg springs. However, the leg spring comes into contact with body tissue with this sort of clip as well as with the previously described clips, so that the material of the spring has to meet the same demands with respect to body compatibility and hygiene than the material of the jaw parts.